Many factors are taken into consideration in the design of egg cartons. Egg protection, resistance to stress or force, stackability, transportability, moisture resistance, aesthetic appearance, print surface area, weight, nestability/detestability, adaptability to accommodate various size eggs, and consistent manufacturing are factors which may be considered to varying degrees in the design of an egg carton.
Filled egg cartons are subjected to multiple adverse mechanical forces and environmental conditions during handling and transport from distribution centers to store shelves, and then from store shelves to consumer homes. They typically encounter automated equipment for packaging, loading, unloading, stacking, restacking and transport. During each of these encounters the goal is to resist egg breakage by stabilizing and holding the eggs in a protected environment, in a carton that can be manufactured in a cost effective manner.
Pulp (paper) egg cartons are stiff and rigid when dry, i.e., under low humidity conditions. However, after being moved in and out of refrigeration, or with a change in the weather, pulp cartons become soggy and do not retain their shape. The dimensional stability of the cell pocket structure is lost. Also, because pulp cartons tend to have very stiff locking flaps and hinges, this creates closing and handling issues for the egg processors. Often, the lid does not line up with the base tray due to the stiff hinge, resulting in cartons which are not level in the closed position. Both problems lead to excessive loading, defective protection and egg breakage issues.
Plastic egg cartons have been provided with flexible walls between the cell pockets to protect the eggs and stop the eggs from going into adjacent cell pockets. However, during handling, such as loading cases (groups of stacked egg cartons) onto a grocery pallet, and stacking the cases 5 to 6 high on the pallet, and/or while being thrown onto the pallets and bumping into each other, the cartons are subjected to considerable compressive and lateral impact forces. The eggs can come out of their cell pockets and make contact from a hard side impact blow. Also, when scanning bar codes on lid tops, the eggs can be displaced and make contact.
Thus, there is need for an improved egg carton construction to provide better egg protection while encountering the adverse mechanical forces and environmental changes that typically occur during packaging, transportation and storage.